Frequency responsive network



June 17, 1947. R. s. YEANDLE 2,422,513

FREQUENCY RESPONSIVE NETWORK 7 Filed Dec. 7, 1944 UTILIZATION SOURCE 0F VAR/ABLE FREQUENCY WA V58 Inventorb y His Attorney Patented June 17, 1947 FREQUENQY RESPONSIVE NETWORK Ralph S. Yeandle, Schoharie, N. Y., assignor to General Electric Company,

New York a corporation of 7 Application December 7, 1944, Serial No. 567,110

7 Claims.

My invention relates to frequency responsive :networks, and more particularly to Wide band "invention, therefore, is particularly well adapted for th demodulation of frequency modulated video signals in television apparatus.

It is a general object of my invention to provide a new and improved wide band frequency responsive network.

It is a further object of my invention to provide a newand improved Wide band frequency discriminating circuit whichexhibits a high degree of linearity of frequency response.

It is a more specific object of my invention to provide means for increasing the band width and improving the linearity of frequency response in a frequency responsive network comprising a pair of oppositely mistuned series resonant circuits connected in parallel. Y

My invention itself will be more fully understood and its objects and advantages further appreciated by referring now to the following detailed specification taken in conjunction with the accompanying drawing, in which Fig. 1 is a schematic circuit diagram of a frequency responsive network embodying my invention in one form, and Fig. 2 is a schematic circuit diagram of a frequency responsive network embodying my invention in another form.

Referring now to the drawing, and particularly to Fig. 1, I have shown an amplifier I having a cathode 2 connected to ground and a control electrode 3 supplied with electric oscillations of variable frequency from a source 4 through a coupling condenser to. It will be understood, of course, that the source of oscillations 4 may pro- ..vide, oscillations modulated in frequency about a predetermined mean frequency in accordance a non-resonant output circuit including a load resistor 6, and the amplified output voltage is supplied through a coupling capacitor 1 to a fre- :quency discriminating circuit including an inductive impedance 8 and a pair of opposed rectifying circuits 9 and Ill. The rectifying circuits 9 and u III include separate inductive impedances II and I2, respectively, connected together at one terminal and having their other terminals connected respectively to the anodes I3 and I4 of a pair of rectifying diodes I5 and I6, respectively. The cathodes I! and I8 of the diodes I5 and I6, respectively, are connected to the electrically remote terminals of a pair of load resistors I9 and 20 having their opposite terminals connected together. The rectifying circuits 9 and II] have a common return path from the common terminal of the load resistors I9 and 20 through a resistor ZI to the common terminal of the impedances II and I2. The inductances I I and I2 are shunted by loading resistors 22 and 23, respectively. The inductance 8 is connected between the coupling condenser I and the common terminal of inductances II and I2.

, The cathode I8 of the diode I6 is connected to ground, and the cathode I! of the diode I5 is connected through a coupling condenser 24 to the control electrode 25 of a signal amplifying discharge device 26. The discharge device 26 includes also a grounded cathode 21 and an anode 28 connected to an output circuit including a load resistor 29. The voltage across the load resistor 29 is supplied through a coupling condenser 30 v to a suitable utilization device 3I.

In operation, it is believed that the stray circu capacitance shunted across the remote terminals of the separate inductive elements I I and I2 is suflicientto form with these elements a parallel resonant circuit tuned approximately to a predetermined mean frequency within the band of frequencies supplied from the source 4. Such stray circuit capacitance has been illustrated by capacitors Ila and In in dotted lines shunted across the inductors II and I2, respectively. It will, of course, be understood that, if necessary and desirable, additional capacitance may be connected between the anodes I 3 and I4 of the diodes I5 and Hi to effect the proper parallel tuning,

The circuit of Fig. 1 includes also a pair of oppositely mistuned series resonant circuits connected in parallel circuit relation between the output terminal of the coupling condenser I and ground. One of these circuits includes the common inductance 8, the inductance II, and the interelectrode capacitance of the discharge devices I5 and 26. Such interelectrode capacitance has been illustrated by capacitors I51; and 26a in dotted lines shunted across the devices I5 and 26v respectively. The other series resonant circuit includes the common inductance 8, the induct ance I2, and the interelectrode capacitance of the diode discharge device I6. The interelectrode capacitance of the diode I6 is illustrated by a capacitor [6a in dotted lines shunted across the device IS. The values of inductance and capacitance in these two series resonant circuits are so proportioned that the circuits are tuned to frequencies slightly displaced to either side of the predetermined mean frequency. Such tuning is controlled by proportioning of the inductances I l and lz andua'lso by'proportioning of the capacitance between the electrically remote terminals of these inductances and ground. It will of course be understood by those skilled in the art that, if desired, the interelectrode--capacitance of the discharge devices in these series resonant circuits may be supplemented by "a'dditi'erial capacitance "points of the rectifier input and output circuits, I

rhave obtained an increased ratio of band width to percent nonlinearity at no reduction of output.

It is believed that this improved operation results Connected between the F4 moref'e'fidtive of the tuned irground. The resistors 22 and 23 are included to load the series resonant circuits to suchanextent that current of approximately the same'intensity flows in each series circuit at its resonant f-requency. It will of course be understood by those skilled in the art that'ieither .one'or both 50f the resistors 22,23 may,'in a particular case,=b'e;found unnecessary.

It will now be evident from the foregoing description that, "when oscillations'of a predetermined mean frequency 1midW-ay between the :resonant frequencies of the two series, resonant circuits are supplied to the discriminating circuit, the voltages appearing across the inductances I l and 12 will be approximately equal, so that the rectified voltages across the load resistors 19 and :20 'will be approximately equal. Since the rectifier circuits .9 and HI are'connected in opposing relation, 'equal unidirectional potentials appear at thewremote terminals ofrthe tresistors'lfi and "'20 when the voltage drops across the resistors are equal. If now the frequency of the oscillations "supplie'difrom the source 4 varies in one direcamount corresponding to the direction "and 1 amount of frequency variation from the nrean :rreque'ncy of the oscillations "supplied by "the Althougnthe theory "of operation "of the inductance 8 which is common to'the two series resonant circuits is not fully understood, it has been found in practicethat the presence "'of'this common inductance permits the use of :a greater band width in the inductance's H and 12 for a given 'overalhdi'scriminator band width, and appears also to facilitate a smoother transfer of "energy between the indu'ctances "H and iZfas the "frequ'en'cyo'f oscillations "changes Withintheband. Accordingly,"therefore; the inductance 8 increases 'the' band width and improves the degree of linear- "i'ty offrequency'resp'onse.

I AtFig. 2,'I have shownanother embodiment'of my invention in which the common return impedance in the rectifying circuits 'S'land lll'is an '1. In all other respects, the circuit of Fig. 2 is similar to that shown at Fig. '1, and like parts have been assigned the'same reference numerals. T-he operation of Fig. 2' is alsoessentially the same 31$ that of 1. The bandwidth o'f th'e "oi-mull;

wcuit comprisin a source of electric *oscilla cuits and the elimination of resistance divider tcirouits formed, .for example, by the resistors l9 and 2| and the resistors 20 and 2| of Fig. 1.

While I have described only certain preferred embodiments of my invention by way of illustra tion many other modifications will occur to those skilled "in the art "and I therefore wisnt'o have'it understood :that'I intend in theappenied claims to cover all such modifications as fall within the truespirit and scope'of my invention. What I claim as new and desire to se'cureby Letters Patent of the United Statesisz '1. Awi'de'band frequency discriminating'circuit comprising a source "of electric oscillations'vaiiiable in frequency over a predeterminedbandbf frequencies, apairrof'serie's resonant circuit 'connected to said source and including a common inductive impedance and a'p'air of separate inductive impedances, said series resonant circuits.

being oppositely 'mistuned with respect to ajoredetermined mean frequency within said he; i To! frequencies, and a pair of opposed Ire'ctify' gencuits connected 'acrossisaidseparate inducti 11m- ,pedances and including separate load resistors having acommon'terminal.

. '2. A wideband frequency discriminating circuit comprising a source of electric oscillations variable in frequency over a predetermined time -of frequencies, apai-rlof series resonant circuits c'onnected to said source and including a common inductive'el'ement :and a pair of separate inductances, said separate --inductances having a nomm'on terminal connected to *one terminal of said common inductive elementa-rrd having theirvre- *mote terminals capacitivel-y coupled for parallel resonance at a predetermined mean frequency within said --ba-n-d, said series 'resonant eironits being oppositely mistuned "with respect rto sai'd mean frequency-and a pair or opposedPrectifying circuits connected across said-separate .mductan'ce's and "including separate wload resistorshaving a common terminal, thereby ito'provide aeross .remoteterminals of said resistors the difference of the rectified voltages appearinga'cross'said'iinductances. j

3; A wide band frequency rlis'criminating variable in frequency over a predetermined new of frequencies, a pair or opposed'rectifyingfl'circuits having a common portion and'ilri'ciu'rlin g separate load resistors having a common iter- "mina'l, separate inductive 'irnpedancereiements in said rectifying'circui'ts, a cominonrinductive pedance connectedbetween-said "source common portion or said rectifying encore. and

means connectin'g'sai'd separate' inductive'impeiiance elements and "saidcommdn in diictiv Jim- 'zpedanc'e in separate series resonantcircui'ts I nected across said source and oppositely mistuned with respect to a predetermined mean frequency within said band of frequencies.

4. A wide band frequency discriminating circuit comprising a source of electric oscillations variable in frequency over a predetermined band of frequencies, a pair of opposed rectifying circuits having a common inductive impedance and including separate load resistors having a common terminal, separate inductive impedance elements in said rectifying circuits, a second common inductive impedance connected between said source and said first common inductive impedance to supply oscillations from said source to said rectifying circuits, and means connecting said second common impedance and said separate impedance elements in separate series resonant circuits connected in parallel across said source and oppositely mistuned with respect to a predetermined mean frequency within said band of frequencies.

5. A Wide band frequency discriminating circuit comprising a source of electric oscillations variable in frequency over a predetermined band of frequencies, a pair of opposed rectifying circuits including a common resistance and a pair of load resistances having a common terminal, separate inductive impedance elements in said rectifying circuits, a common inductive impedance connected between said source and said common resistor to supply oscillations from said source to said rectifying circuits, and means connecting said separate inductive impedance elements and said common inductive impedance in separate series resonant circuits connected across said source and oppositely mistuned with respect to a predetermined mean frequency within said band of frequencies.

6. A wide band frequency discriminating circuit comprising a source of electric oscillations variable in frequency over a predetermined band of frequencies, a pair of opposed rectifying circuits including a common impedance element and a pair of load resistors having a common terminal connected to one terminal of said impedance element, separate inductive impedances in said rectifying circuit having a common terminal connected to the other terminal of said common impedance element, and a common inductiv impedance connected between said source and the common terminal of said separate inductive impedances, thereby to form with said separate impedances and the stray circuit capacities a pair of series resonant circuits connected in parallel and tuned to resonance at spaced apart frequencies in said band of frequencies.

7. A wide band frequency discriminating circuit comprising a source of electric oscillations variable in frequency over a predetermined band of frequencies, a pair of opposed rectifying circuits including a common impedance element and a pair of load resistors having a common terminal connected to one terminal of said impedance element, separate inductive impedances in said rectifying circuits having a common terminal connected to the other terminal of said common impedance element, the stray capacity of said rectifying circuits in shunt with said separate inductive impedances being sufiicient to tune said inductive impedances to a mean frequency within said band, and a common inductive impedance connected between said source and the common terminal of said separate inductive impedances, thereby to form with said separate inductive impedances and the stray circuit capacities a pair of series resonant circuits connected'in parallel and oppositely mistuned with respect to said mean frequency.

RALPH S. YEANDLE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,286,378 Roberts June 16, 1942 2,293,501 I-Iansell Aug. 18, 1942 2,304,377 Roberts Dec. 8, 1942 

